Populations of cod, long a mainstay for New England fisheries and an iconic inhabitant of the ecosystem of the Gulf of Maine, are near collapse, and scientists are pointing the finger of blame at climate change.
Despite conservation efforts, including strict fishing quotas, cod stocks have fallen to between three and four percent of possible sustainable levels because climate change has warmed gulf waters much faster than is seen in the rest of the Atlantic Ocean, researchers say.
The Gulf of Maine has warmed an average of 0.4 degrees Fahrenheit every year, a rate faster than seen in 99.9 percent of the rest of the Atlantic, they note.
Decreased reproduction and increased mortality among the once abundant Atlantic cod has been the result of those rising temperatures coming on top of decades of overfishing, they report in the journal Science.
The warming has been associated with fluctuations in the path of the Gulf Stream and oscillations in climate in both the Atlantic and Pacific Oceans, they explain.
The collapse has occurred even though fisheries managers put a number of restrictions and quotas on harvesting cod in place in 2010 in the face of already-depleted stocks.
"Managers kept reducing quotas, but the cod population kept declining," says study lead author Andrew Pershing of the Gulf of Maine Research Institute. "It turns out that warming waters were making the Gulf of Maine less hospitable for cod, and the management response was too slow to keep up with the changes."
Quotas were set too high because managers were not taking into account the effect of increasing temperatures, he says, so even though fishermen were abiding by the quotas, they were still, in effect, overfishing, he says.
"This creates a frustrating situation that contributes to mistrust between fishermen, scientists, and managers," Pershing points out. "The first step toward adapting fisheries to a changing climate is recognizing that warming impacts fish populations."
Atlantic cod are a cold-water species found from the U.S. northeast coast north to Canada and across the North Atlantic as far as the Barents Sea north of Russia.
The Gulf of Maine sits at the lower edge of the species' range, so warming there will reduce the gulf's capacity to support the cod and will result in smaller populations, with a follow-up on the impact on fisheries, researchers say.
Whether or not gulf populations of the cod can recover will depend not just on sound fisheries management but on taking into account future temperature trends, they add.
